In 2008, the NASA/ESA Hubble Space Telescope discovered carbon dioxide in the atmosphere of a Jupiter-sized planet orbiting another star. This was seen as an important step in the search for evidence of life on other worlds.

Some 300 planets have so far been discovered in orbit around distant stars. Unfortunately, these extrasolar planets are so faint and so far away that it is extremely difficult to study them. However, with modern instruments, scientists are gradually beginning to learn more about these alien worlds and the gases which make up their atmospheres.

Carbon dioxide is the gas that plants give out during the night and use to grow. Animals and humans breathe it out every few seconds. As one of the main greenhouse gases, it traps heat and helps to warm up a planet. Carbon is also the basis of so-called organic compounds, which are among the building blocks of life. Now Hubble has shown that we can detect carbon dioxide on distant planets and estimate how much is present. This is a major advance in the long-term effort to find out what these worlds are made of and if they could support life.

The planet, called HD 189733b, is too hot for life. However, it is a good planet to observe because it disappears behind its companion star once every 2.2 days. By studying the regular changes in the light reaching Earth, scientists can analyse the planet’s atmosphere. Water vapour and methane have already been found. The new Hubble observations prove that the basic chemistry for life can be measured on planets orbiting other stars.

Are we alone?

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Life around other stars (http://www.esa.int/esaKIDSen/SEMNOIWJD1E_LifeinSpace_0.html)